ABSTRACT As many as 20% of patients undergoing open heart surgery can have immediate or delayed postoperative cardiovascular compromise. In the immediate period, cardiac function is often monitored using a pulmonary artery catheter and an arterial line. This helps prevent problems in cardiac function and output by noting changes from the information gathered from these catheters that allow immediate assessment and treatment. However, these devices, particularly the pulmonary artery catheter, present significant risks to patients including fatal arrhythmias, perforation of blood vessels or the heart, bleeding into the airway, entanglement and thrombus formation. If the patient is very sick, it is very common to keep this catheter in place for a prolonged period or exchange it on a regular basis. However, indwelling lines carry a high risk of bloodstream infection and sepsis. Furthermore, patients typically are kept in bed until the pulmonary artery catheter is able to be removed. To add to this, the measurement of cardiac output from this catheter is often unreliable and inconsistent. This can make being able to treat the patient appropriately difficult and potentially dangerous. Our goal of this proposal is to design, fabricate, and test a device placed on the surface of the aorta and pulmonary artery during open heart surgery that can provide information on cardiac function, while avoiding the risk of indwelling lines. The envisioned device will: 1) be easily deployed; 2) avoid risk of infection by being on the surface of the vasculature; 3) provide accurate and precise measurements of cardiac function; 4) provide a long-term postoperative solution that is safe and easily removable. The core technology will be a highly sensitive crack-based strain sensor that can be multiplexed into arrays and integrated with transient flexible adhesive hydrogels. Strain sensors integrated with adhesive hydrogels will measure pressure waveforms and flow rates; data that can be used to accurately calculate cardiac output. Sensor arrays will be tested using in vitro and ex vivo models to calibrate measurements with cardiac output. Finally, we will compare the in vivo measurements of flexible strain sensors with that of pulmonary artery catheters using an acute infarct model in swine. The overall performance of transient flexible adhesive strain sensor arrays will be benchmarked to pulmonary artery catheters, the existing standard of care.